The present invention relates to a heavy duty tire having an improved tread structure capable of preventing uneven wear.
In recent years, tread patterns comprising blocks such as block pattern, rib-block pattern and the like are widely used in not only passenger car tires but also heavy duty tires such as pneumatic tires for trucks, buses and the like.
In the heavy duty tires, the load of each block is relatively heavy, and accordingly uneven wear is very liable to occur. For example, uneven wear between axially outer part and inner part of a block caused by a difference in the rolling diameter of the tire is liable to occur in axially outer blocks such as shoulder blocks. This type of uneven wear is called shoulder wear. Uneven wear at the circumferential edges (heel and toe) of a block is called heel and toe wear, and this type of uneven wear occurs in every block, but the degree is higher in the axially outer blocks such as shoulder blocks.
In order to improve the shoulder wear, it has been proposed to subdivide each shoulder block into an axially outer narrow width part and an axially inner wide part by a narrow groove extending straight in the tire circumferential direction so as to concentrate the wear on the axially outer narrow width part.
In this proposition, however, the heel and toe wear can not be improved, and as the rigidity of the axially outer narrow width part is low, this part is liable to be torn off.
Therefore, it is an object of the present invention to provide a heavy duty tire in which the heel and toe wear as well as shoulder wear is effectively improved and the resistance to tear-off is increased.
According to the present invention, a heavy duty tire comprises
a pair of axially outermost circumferential rows of shoulder blocks,
each of the shoulder blocks provided with a circumferentially extending narrow groove,
the narrow groove subdividing the shoulder block into an axially inner wide main part and an axially outer narrow lateral part, wherein
the narrow groove is curved convexly so that the narrow lateral part is narrower in a substantially middle region than both circumferential end regions in the circumferential direction.
Preferably, the narrow groove has a substantially constant width in the range of from 1.5 to 3.0 mm. The narrow lateral part has a minimum axial width in the range of from 5 to 8% of the average axial width of the shoulder block, and a maximum axial width in the range of from 7 to 12% of the average axial width.